To verify fluid dynamic simulations, flow fields can be visualized by particle image velocimetry (PIV), an instrument relied upon by industrial research in fluid dynamics contexts. In PIV, sequential images of particles seeded into the flow field for this purpose are correlated to obtain vector fields which represent the flow. Proper particle seeding, which is often meticulously tweaked empirically, is necessary to receive good results.
A solution which does not require seed particles is desirable. This being particularly useful for complex channel geometries with strongly differing flows in different regions, as in these situations it may be infeasible to find a particle seeding that satisfies the constraints on particle concentration in all regions simultaneously.